(1) Field of the Invention
The present invention relates to a peeling solution for photo- or electron beam-sensitive resin and to a process for peeling off a photo- or electron beam-sensitive resin using said solution. The present invention is applied for removing a photo- or electron beam-sensitive resin from a substrate.
(2) Description of the Prior Art
As substrates on which a photo- or electron beam-sensitive resin is to be coated, there are, for example, those composed of glass, metal, plastic or ceramic, as well as those consisting of a glass and a thin film (made of a metal or the like) formed thereon. On a case of using, as such a substrate, a photomask blank (hereinafter may be referred to simply as "blank") which is used as a material for photomask in the production of semiconductor integrated circuits (e.g. IC, LSI), there are explained below the conventional peeling solutions for photo- or electron beam-sensitive resin and the conventional processes for peeling off a photo- or electron beam-sensitive resin.
The above mentioned blank consists of a light-transmitting substrate (e.g. polished silica glass) and a light-shielding film (e.g. chromium film) formed on one main surface of the substrate. In producing a photomask from the blank, firstly a photo- or electron beam-sensitive resin such as photoresist, electron beam resist or the like is coated on the light-shielding film of the blank by a coating method such as spin coating or the like.
In the above coating of a photo- or electron beam-sensitive resin on the light-shielding film, it occurs at times that the film of the photo- or electron beam-sensitive resin formed on the light-shielding film of the blank has non-uniform thickness depending upon the resin coating conditions (e.g. temperature) and the resin properties (e.g. viscosity). When such a blank on which a photo- or electron beam-sensitive resin film has been formed in non-uniform thickness is then subjected to a photolithography step or an electron beam lithography step to produce a photomask, the light-shielding pattern formed on the light-transmitting substrate has no constant line width as required and it is impossible to obtain a photomask having a desired light-shielding pattern.
The blank on which a photo- or electron beam-sensitive resin film has been formed in non-uniform thickness is regarded as a blank with a resist of unacceptable film thickness and cannot be used practically. However, when such a blank with a resist of unacceptable film thickness is made of an expensive light- transmitting substrate such as silica glass or the like, the light-transmitting substrate is reutilized by immersing the blank in a peeling solution for photo- or electron beam-sensitive resin to peel off the photo- or electron beam-sensitive resin (the resist) and then peeling off and removing the light-shielding film with a given etching solution. The resulting light-transmitting substrate is repolished and then provided with a new light-shielding film to produce a blank; and a photo- or electron beam-sensitive resin is coated on the light-shielding film.
As the peeling solution used when the photo- or electron beam-sensitive resin to be peeled off hereby is a photoresist sensitive to a light such as ultraviolet light or the like, there has been known the following peeling solutions, that is, a photoresist peeling solution consisting of a mixture of an aqueous hydrogen peroxide and sulfamic acid (Japanese Patent Application Kokai (Laid-Open) No. 13776/1977), a photoresist film remover consisting of a mixture obtained by adding an acid to a persulfate, hydrogen peroxide or hydrogen peroxide adduct (Japanese Patent Application Kokai (Laid-Open) No. 24627/1979), and a photoresist peeling solution consisting of a mixture of acetone and N,N-dimethylformamide (Japanese Patent Publication No. 6101/1982).
The photo- or electron beam-sensitive resin to be peeled off includes, besides the above mentioned photoresists, electron beam resists sensitive to electron beam and the electron beam resists include those of negative type and those of positive type. The electron beam resists of negative type include, for example, an epoxy resin, an unsaturated dicarboxylic acid resin and a polystyrene, and the electron beam of positive type include, for example, a polyolefinsulfone and a polymethyl methacrylate.
As the peeling solution for these electron beam resists, there are known methyl ethyl ketone, hot concentrated sulfuric acid, dimethyl sulfoxide, methylene chloride, etc.
With the above conventional peeling solutions for photoresist or even with the above conventional peeling solutions for electron beam resist, it is difficult to peel off electron beam resists reliably in a short time.
Therefore, a very long time is required when a blank whose light-transmitting substrate is to be reutilized is immersed in a conventional peeling solution for electron beam resist to peel off the electron beam resist and then is treated with a given etching solution to remove the light-shielding film. It is because a very thin resist film remains on the light-shielding film at the time of the peeling of the electron beam resist owing to the strong adhesion of the resist to the light-shielding film and hinders the removal of the light-shielding film.
Meanwhile, a developing solution used in the step of subjecting an electron beam resist of negative type to development can be used also as a peeling solution for that electron beam resist of negative type. However, the above developing solution is expensive and accordingly its use also as a peeling solution is not practical. Further, when the developing solution is used also as a peeling solution as mentioned above, one specific developing solution must be prepared for one specific electron beam resist of negative type, which not only incurs a high cost but also makes the operation complex.
The first object of the present invention is to provide a peeling solution for photo- or electron beam-sensitive resin which can reliably peel off various types of photo- or electron beam-sensitive resins from substrates on which said photo- or electron beam-sensitive resins are coated.
The second object of the present invention is to provide a process for peeling off a photo- or electron beam-sensitive resin, which can reliably peel off various types of photo- or electron beam-sensitive resins from substrates on which said photo- or electron beam-sensitive resins are coated and, when said substrates are photomask blanks, can further facilitate the removal of the light-shielding films of the photomask blanks by an etching treatment to be applied after the peeling of photo- or electron beam-sensitive resin.
Other objects of the present invention will be apparent from the following description.